Objectives: Certain guidelines recommend caution when administering immunotherapy in patients with pre-existing interstitial lung disease (ILD) owing to the high incidence of pneumonitis induced by anti-cancer therapy. A prospective clinical trial assessing the safety of chemoimmunotherapy in patients with small-cell lung cancer (SCLC) and pre-existing ILD is warranted. Therefore, this study evaluated the safety and efficacy of chemoimmunotherapy in patients with extensive-stage (ES)-SCLC and mild idiopathic interstitial pneumonia (IIP)., Methods: In this multicenter prospective trial, patients with ES-SCLC and pre-existing mild chronic fibrosing IIP were recruited. Mild IIP was defined as the exclusion of poor pulmonary function, a definite usual interstitial pneumonia (UIP) pattern, and positivity for autoantibodies in blood tests. The patients received durvalumab, etoposide, and carboplatin every three weeks (induction phase), followed by 1,500 mg durvalumab every four weeks (maintenance phase). The primary endpoint was severe pneumonitis-free rate., Results: Twenty-one patients were included in the analysis. Among them, 13 patients displayed a probable UIP pattern, whereas eight patients exhibited an indeterminate for UIP pattern. Two patients (9.5 %) had pneumonitis of any grade during the induction phase; one had Grade 1 and the other had Grade 5 pneumonitis. No other patient developed pneumonitis during the maintenance phase. The severe pneumonitis-free rate was 95.2 % (95 % confidence interval (CI): 77.3-99.2 %). The median progression-free survival was 5.5 months (95 % CI: 3.6-6.4 months). Median overall survival was 10.7 months (95 % CI: 6.0 months to not reached)., Conclusions: Chemoimmunotherapy is a feasible treatment approach for patients with ES-SCLC and mild IIP., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: [Daichi Fujimoto reports financial support provided by AstraZeneca K.K. Ryota Shibaki received personal fees from AstraZeneca KK, Taiho Pharmaceutical Co. Ltd., Chugai Pharmaceutical Co. Ltd., and MSD KK outside the submitted work. Daichi Fujimoto received grants from AstraZeneca K.K. during the study and personal fees from AstraZeneca KK, Boehringer Ingelheim Japan Inc., Ono Pharmaceutical Co. Ltd., Bristol-Myers Squibb Co. Ltd., Taiho Pharmaceutical Co. Ltd., Chugai Pharmaceutical Co. Ltd., MSD KK, Eli Lilly Japan KK, Kyowa Kirin Co. Ltd., Janssen Pharmaceutical KK, Daiichi Sankyo Co. Ltd., Takeda Pharmaceutical Co. Ltd., and Novartis Pharma KK outside of the submitted work. Eisaku Miyauchi received personal fees from AstraZeneca KK, Boehringer Ingelheim Japan Inc., Ono Pharmaceutical Co. Ltd., Bristol-Myers Squibb Co. Ltd., Taiho Pharmaceutical Co. Ltd., Chugai Pharmaceutical Co. Ltd., MSD KK, Eli Lilly Japan KK, Kyowa Kirin Co. Ltd., Daiichi Sankyo Co. Ltd., Takeda Pharmaceutical Co. Ltd., Merck Biopharma Co. Ltd., Pfizer Inc., Eisai Co. Ltd., Otsuka Pharmaceutical Co. Ltd., Amgen Inc., Thermo Fisher Scientific KK, Nippon Kayaku Co. Ltd., Sysmex Co. Ltd., KYORIN Pharmaceutical Co. Ltd., and Novartis Pharma KK outside the submitted work. Yoko Tsukita received personal fees from AstraZeneca KK, Bristol-Myers Squibb Co. Ltd., Taiho Pharmaceutical Co. Ltd., Chugai Pharmaceutical Co. Ltd., MSD KK, Eli Lilly Japan KK, Daiichi Sankyo Co. Ltd., Eisai Co. Ltd., and Boehringer Ingelheim Japan Inc. outside the submitted work. Daisuke Arai has received personal fees from AstraZeneca KK, Taiho Pharmaceutical Co. Ltd., Chugai Pharmaceutical Co. Ltd., MSD KK, Eli Lilly Japan KK, Ono Pharmaceutical Co. Ltd., Takeda Pharmaceutical Co. Ltd., Merck, and Nippon Kayaku Co. outside the submitted work. Yoshihiko Sakata received personal fees from AstraZeneca KK, Amgen, Boehringer Ingelheim Japan Inc., Bristol-Myers Squibb Co. Ltd., Taiho Pharmaceutical Co. Ltd., Chugai Pharmaceutical Co. Ltd., MSD KK, Eli Lilly Japan KK, Kyowa Kirin Co. Ltd., Takeda Pharmaceutical Co., Ltd., and Novartis Pharma KK outside the submitted work. Naoki Shingu received personal fees from AstraZeneca KK, Chugai Pharmaceutical Co. Ltd., Bristol-Myers Squibb Co. Ltd., Takeda Pharmaceutical Co. Ltd., and MSD KK outside the submitted work. Takashi Kijima received personal fees from Chugai Pharmaceutical Co. Ltd. outside the submitted work. Go Saito received personal fees from AstraZeneca KK, Taiho Pharmaceutical Co. Ltd., Chugai Pharmaceutical Co. Ltd., MSD KK, Ono Pharmaceutical Co. Ltd., Pfizer, Daiichi Sankyo Company, and Novartis Pharma KK outside the submitted work. Yuki Sato received personal fees from AstraZeneca KK, Ono Pharmaceutical Co. Ltd., Bristol-Myers Squibb Co. Ltd., Taiho Pharmaceutical Co. Ltd., Chugai Pharmaceutical Co. Ltd., MSD KK, Eli Lilly Japan KK, Kyowa Kirin Co. Ltd., Daiichi Sankyo Co. Ltd., and Takeda Pharmaceutical Co. Ltd., Pfizer Inc., Nippon Kayaku Co., Ltd., and Novartis Pharma KK outside the submitted work. Shinya Sakata received personal fees from AstraZeneca KK, Taiho Pharmaceutical Co. Ltd., Chugai Pharmaceutical Co. Ltd., and Takeda Pharmaceutical Co. Ltd. outside the submitted work. Yoshihiko Taniguchi received personal fees from AstraZeneca KK, Bristol-Myers Squibb Co. Ltd., and Chugai Pharmaceutical Co. Ltd. outside the submitted work. Akito Hata has received personal fees from AstraZeneca KK, Taiho Pharmaceutical Co. Ltd., Chugai Pharmaceutical Co. Ltd., Eli Lilly Japan KK, Pfizer Inc., and Boehringer Ingelheim outside the submitted work. Hirotaka Matsumoto received personal fees from AstraZeneca KK, Taiho Pharmaceutical Co. Ltd., Chugai Pharmaceutical Co. Ltd., MSD KK, Takeda Pharmaceutical Co. Ltd., Nippon Kayaku Co. Ltd., Ono Pharmaceutical Co. Ltd., and Boehringer Ingelheim outside the submitted work. Nobuyuki Yamamoto has received personal fees from AstraZeneca KK, Chugai Pharmaceutical Co. Ltd., MSD KK, Ono Pharmaceutical Co. Ltd., Daiichi Sankyo, Taiho Pharmaceutical Co. Ltd., Takeda Pharmaceutical Co. Ltd., Boehringer Ingelheim Japan Inc., Pfizer Inc., Amgen Inc., Janssen Pharmaceutical KK, Terumo, Eli Lilly Japan KK, Novartis Pharma KK, Merck Biopharma, Guardant Health Japan, Accuray Inc., AbbVie, Kyorin Pharmaceutical Co. Ltd., Tsumura & Co., and Miyarisan Pharmaceutical outside the submitted work. Other authors declare that they have no competing financial interests or personal relationships that could have influenced the work reported in this study.]., (Copyright © 2024 Elsevier B.V. All rights reserved.)